1. Field of the Invention
This invention discloses the formulation and use of advanced solid-media chemical compositions designed and intended to enhance the removal of halogenated organic contaminants and the oxidized forms of inorganic contaminants from industrial wastes, soils, sediments, sludges, ground waters, surface waters, and the like. In particular, this invention provides an improved means of promoting the anaerobic, biologically mediated degradation, transformation and/or detoxification of a broad range of recalcitrant and/or hydrophobic halogenated organic and inorganic contaminants in the environment, including, but not limited to, organochlorine pesticides such as DDT and toxaphene, arsenic and/or arsenate-based pesticides, polychlorinated biphenyls (PCBs), dioxins, halogenated organic solvents such as perchloroethylene, trichloroethylene, trichloroethane and freon, and toxic inorganic contaminants such as cyanide, hexavalent chromium and the oxidized forms of other toxic heavy metals. This invention provides improved means for (i) promoting the solid-phase extraction of recalcitrant, hydrophobic contaminants from contaminated media and enhancing the bioavailability and biogeochemical reactivity of such contaminants, (ii) creating, enhancing and maintaining both strongly anaerobic and highly reducing conditions favorable to the biodegradation, dehalogenation, transformation and/or detoxification of these contaminants by naturally occurring microorganisms, (iii) providing a source of complex anaerobic electron acceptors, and nutrients to promote the growth of these contaminant-degrading microorganisms, and (iv) providing sources of inoculum of different types of naturally occurring microorganisms which act to directly undertake or indirectly promote the biodegradation, dehalogenation, transformation, and/or detoxification of these contaminants. This invention specifically reveals a cost-effective and relatively simple to use improved inorganic composition, and methods for its use thereof, that is designed to promote one or more of the aforementioned processes in the treatment of environmental contamination.
2. Description of Prior Art
Soil and ground-water pollution caused by chemical contaminants released into the environment is a well documented, world-wide problem. Such chemical contamination is associated with many different types of industrial activities conducted over the last two centuries. Common environmental contaminants include several different types and forms of petroleum hydrocarbons, halogenated organic compounds including solvents (e.g., tetra- and trichloroethene, methylene chloride), pesticides (e.g., DDT and toxaphene), polychlorinated biphenyls (i.e., PCBs) and heavy metals and other inorganic contaminants such as cyanides. The available toxicological data indicates that many of these contaminants, (in particular many of the halogenated organic compounds), are either carcinogenic or potentially carcinogenic to both man and animals. In addition, the available environmental and ecological data have shown that many of these contaminants tend to persist in the environment for long time periods and, consequently, they tend to accumulate in the tissues of biological organisms up the food chain. The long-term stability and extremely slow degradation of many such environmental contaminants presents a substantial, long-term hazard to human health and the environment throughout the industrialized world.
Many of the so-called conventional methods for the remediation or clean-up of chemically contaminated wastes, waters, soils and sediments have generally involved either the physical removal of the contaminated media or the simple mass transfer of the contaminants from one media (e.g., soil) to another (e.g., air). In general, such physical-treatment technologies do not involve the chemically and/or biologically mediated breakdown, transformation or detoxification of the contaminants. Two of the most common categories of physical environmental remediation technologies are the excavation of contaminated soils and the pumping and subsequent treatment of contaminated ground water. The excavation of contaminated soils is often followed by their disposal in a landfill, which can pose a potential long-term risk to the environment. Many ground-water pump-and-treat processes involve the simple mass-transfer or xe2x80x9cstrippingxe2x80x9d of the contaminants from the water into the air. Another common physical-treatment method involves the use of granular activated carbon (GAC) reactors to treat chemically contaminated waters. When contaminated water is passed through a GAC reactor, the contaminants are physically adsorbed onto the carbon particles, thereby producing another contaminated media which requires subsequent disposal and/or treatment. Each of these physical-treatment technologies share the same disadvantagexe2x80x94i.e., they do not reduce the actual amount or toxicity of the chemical contaminants, but rather they simply move the contamination from one place to another or from one media to another.
Another well-known physical treatment process which involves the thermal treatment or incineration of the contaminated materials can be an effective albeit expensive means of breaking down the molecular structure of the contaminants into non-hazardous products. For example, high-temperature incineration is known to be effective for the treatment of materials containing pesticides and PCBS. Thermal-treatment methods require the use of sophisticated and operation-and-maintenance-intensive equipment, the costs of which are passed on to industry in the form of expensive unit costs for soil treatment. In addition, because thermal-treatment processes are rarely, if ever, one-hundred-percent effective in the destruction of the contaminants, they can produce atmospheric emissions of contaminants or the toxic by-products of contaminants. For example, the incomplete incineration of PCBs can produce dioxins, which in turn are significantly more toxic than their xe2x80x9cparentxe2x80x9d PCB compounds.
A third category of environmental-remediation treatment technologies, bioremediation, involves the use of microorganisms to convert chemical compounds into innocuous or less harmful chemical compounds. Bioremediation technologies generally have lower costs associated with their use and implementation than do the competing physical technologies. Bioremediation technologies are also more adaptable to different types of contamination problems and variations in field conditions than are physical-treatment technologies.
The most promising bioremediation technologies provide the additional capability of treating contaminated media in-situ, i.e., in place, without the need for ground-water pumping or soil excavation. Current trends in bioremediation technology indicate that the most technically feasible and commercially successful bioremediation technologies are those which utilize indigenous or xe2x80x9cnativexe2x80x9d contaminant-degrading bacteria (CDB), fungi and other microorganisms which are naturally present in the contaminated media. The presence of CDB in many different types of environments has been extensively reported in the scientific literature. There is an extensive body of prior art literature and patents concerning various means of using both aerobic and anaerobic CDB (as well as engineered or cultured bacteria) to biodegrade organic contaminants in water, soil and industrial wastes. For example, it has been reported that native Alcaligenes spp., Pseudomonas spp., and Enterobacter spp. can degrade a number of pesticides and polychlorinated biphenyls (Nadeau et al., 1994, Applied and Environmental Microbiology; Aislabie et al., 1997, New Zealand Journal of Agricultural Research; Galli et al., 1992, Pseudomonas: Molecular Biology and Biotechnology). Given the significant advantages of using native microorganisms versus the need to introduce cultured or engineered microorganisms, methods which involve the use of artificially introduced microorganisms (e.g., U.S. Pat. No. 5,932,472) are declining in favor within both the scientific and engineering communities. Recent trends in the art and literature acknowledge a growing understanding of the use of anaerobic biological processes in the treatment of many different types of contaminants that are otherwise recalcitrant under aerobic conditions. In particular, trends in the art reflect a growing understanding of the need and importance of achieving and maintaining anaerobic conditions and other factors which favor the biologically mediated reduction, biodegradation, transformation and/or detoxification of recalcitrant organic and inorganic contaminants in the environment.
The current understanding reflected by the art is that the recalcitrant nature of many halogenated organic contaminants, polynuclear aromatic hydrocarbons (PAHs), other heavy (i.e., high-molecularweight) hydrocarbons, and the like is related to the hydrophobic nature and extremely low solubilities of the contaminants. Consequently, the xe2x80x9cbioavailabilityxe2x80x9d of these contaminants, i.e., their availability to biological degradation processes mediated by microorganisms, is extremely limited under most environmental conditions. The prior art describes the use of chemical methods (e.g., Szejtli, et al., U.S. Pat. No. 5,425,881) and thermal methods (e.g., Rothmel, et al., U.S. Pat. No. 5,567,324) to increase bioavailability. For a number of chemically complex hydrophobic chlorinated organic compounds, such as pesticides and PCBs, the prior art has suggested that the higher molecular weight (i.e., more chlorinated) compounds can not be practically biodegraded and thus bioremediation techniques have been all but abandoned with respect to the treatment of such compounds in the environment. For example, through laboratory and pilot-scale experiments directed at the investigation of bioremediation processes on Hudson River sediments contaminated with PCBs, General Electric (GE) researchers determined that the PCBs associated with the sediments consisted of both a labile (i.e., biologically usable) fraction and a resistant (i.e., refractory or relatively non-biologically usable) fraction (General Electric Company, 1992). The labile fraction was described by GE as the lower-molecular weight, less-chlorinated congeners that could be readily desorbed from the sediments. GE described the resistant fraction as the higher-molecular weight congeners that were adsorbed or otherwise bound to the natural organic matrix of the sediments thus greatly limiting their bioavailability to microorganisms. Inoculations with a purified PCB-degrading bacterial strain failed to improve the rate or extent of PCB reduction in the GE experiments. In addition, the GE study did not investigate any means or methods to try to increase the bioavailability of the most recalcitrant PCB congeners. Furthermore, the GE research failed to address or disclose methods or means involving the use of solid or liquid compositions to create and control optimal anaerobic conditions and Eh-pH conditions favorable to the biodegradation of the PCBs. Alternatively, and in contrast to the present invention, further studies along the lines of GE""s prior work have all but given up on the biodegradation of the resistant PCB congeners and have instead focused on the potential reduction of the environmental risks posed by these congeners via the long-term biostabilization of these congeners in the sediments (Gan and Berthouex, 1994; Alcock et al., 1995). These studies have further suggested that PCB biodegradation continues to occur slowly over an extended time frame as specific PCB congeners become bioavailable (Gan and Berthouex, 1994; Alcock et al., 1995).
Unlike the present invention, U.S. Pat. No. 5,789,649 to Batchelor et al. (E.I. du Pont de Nemours and Company) discloses a means for the degradation of contaminants in soil consisting of adding both a xe2x80x9cstabilizing agentxe2x80x9d and a xe2x80x9creductive zero-valent metal and metal catalyst.xe2x80x9d In the process disclosed by Batchelor et al. (U.S. Pat. No. 5,789,649), the contaminants are first stabilized within the solid matrix using a xe2x80x9cstabilizing agent,xe2x80x9d such as that comprised of mixtures of bentonite clay and iron chloride. Batchelor et al. (U.S. Pat. No. 5,789,649) further disclose the use of a xe2x80x9creductive zero-valent metal and metal catalystxe2x80x9d which provides for a xe2x80x9cmetallic couplexe2x80x9d which leads to the reductive dehalogenation of the halogenated organic compounds and the consequent reduction of their concentration. Current understanding, however, reflects the need to extract, desorb, solubilize or otherwise remove the contaminants from the solid or non-aqueous phases in order to increase the bioavailability of the halogenated compounds to microorganisms to facilitate their biodegradation. Batchelor et al. (U.S. Pat. No. 5,789,649) do not disclose the chemical compositions, methods or means of the present invention.
U.S. Pat. No. 5,266,213 to Gillham and peer-reviewed literature by Gillham and O""Hannesin (Ground Water, 1994) disclose a remediation process limited to the treatment of ground water contaminated with chlorinated aliphatic compounds wherein the contaminated water is fed through a trench or tank containing a metal, such as iron fillings, under strict exclusion of oxygen (Eh values xe2x88x92100 to xe2x88x92200 mV). The contaminant breaks down under such reducing conditions into innocuous by-products. Based on the results of tests in which sodium azide was added to the columns, Gilham et al. concluded that the degradation process was abiotic in nature. Gillham (U.S. Pat. No. 5,266,213) opined that the degradation process involved the abiotic, electrochemical reduction of the iron and the associated reductive dechlorination of the organic compounds from the electrons produced by the reduction of the iron. However, the present invention discloses compositions and methods whereby iron reduction (and the reduction of other metals) coupled to the reductive-dehalogenation of organic contaminants is a biologically mediated process. Therefore, Gillham (U.S. Pat. No. 5,266,213) and Gillham and O""Hannesin (Ground Water, 1994) do not disclose the present invention.
Sayles et al. (Environmental Science and Technology, 1997) investigated the utility of using zero-valent iron (e.g., granular iron filings and the like) to dechlorinate DDT and related compounds in an anaerobic aqueous environment. Sayles et al. also acknowledged the importance of providing for a large surface-area of reactive iron, such as that which could be facilitated by the use of a fine particulate or powdered forms of iron. Sayles et al. also investigated the use of a surfactant to increase the availability of DDT to the xe2x80x9cchemicalxe2x80x9d reactions catalyzed by the zero-valent iron. Like Gillham (U.S. Pat. No. 5,266,213) and Gillham and O""Hannesin (Ground Water, 1994), Sayles et al. do not disclose the use of more than a single inorganic amendment (i.e., in addition to the iron) to help optimize or control Eh-pH conditions. Like Giliham (U.S. Pat. No. 5,266,213) and Gillham and O""Hannesin (Ground Water, 1994), Sayles et al. also fail to acknowledge, investigate or otherwise disclose biologically mediated reductive-dehalogenation methods, means or compositions. Therefore, Sayles et al. does not disclose the present invention.
U.S. Pat. Nos. 5,411,664 and 5,618,427 to Seech et al. (W. R. Grace) disclose practically identical methods for the respective biodegradation of halogenated aromatic compounds (US. Pat. No. 5,411,664) and nitroaromatic compounds (U.S. Pat. No. 5,618,427). Both patents disclose the use of both fibrous organic matter and multi-valent metal particles to the contaminated media. These patents discuss adding these amendments to soil, water, or sediments and subsequently incubating these media under anaerobic conditions conducive to the growth of the indigenous contaminant-degrading microorganisms. The patents to Seech et al. disclose that the fibrous nature of the plant materials used is important to enable the organic contaminant to become absorbed into the fibrous structure of the plant material which enhances the extent of contaminant removal from the environmental media. Seech et al. also disclose the use of multi-valent metals, (preferably iron or magnesium), in combination with the fibrous plant matter wherein the multi-valent metals are specifically capable of being both oxidized and reduced back and forth under normal environmental conditions. Seech et al. do not discuss or disclose the potential problems associated with the precipitation of metallic oxyhydroxides and metallic carbonates or the tendency of such precipitates to lead to unfavorable Eh-pH conditions for the anaerobic, reductive dehalogenation of recalcitrant organic contaminants, let alone methods, means or compositions to overcome these problems. Consequently, Seech et al. do not disclose the present invention.
U.S. Pat. No. 5,078,899 to Garrison (Idaho Research Foundation, Inc.) discloses a method of treating mine drainage water to remove ferric hydroxide, which is not the subject of the present invention. Although Garrison (U.S. Pat. No. 5,078,899) does not disclose the present invention, the present invention provides for the beneficial use of the wastes produced by the oxidation of mine drainage waters, e.g., ferric oxyhydroxides and the like, as a component of the inorganic chemical composition disclosed herein.
In accordance with the present invention there is provided novel and improved solid-chemical compositions and associated methods and means for the use of said compositions to promote the anaerobic, biologically mediated, degradation, transformation, and/or detoxification of recalcitrant organic and inorganic environmental contaminants present in solid and liquid wastes, soils, sediments, and water into non-hazardous and/or less hazardous by-products. The principles of this invention provide for the relatively rapid and cost-effective anaerobic, biologically mediated decontamination of halogenated solvents such as tetrachloroethene (PCE), trichloroethene (TCE), 1,1,1-trichloroethane (1,1,1-TCA), freon and the like; other recalcitrant halogenated organic compounds such as DDT, toxaphene, PCBs, dioxins, and the like; arsenic-based pesticides; and recalcitrant inorganic contaminants such as cyanides, hexavalent chromium, the oxidized forms of other toxic transition metals, and the like.
A further object of the invention is to present means by which to overcome the disadvantages associated with not only the traditional methods of remediation previously described, but also the limitatioris of other more recent and/or technically advanced methods and means of chemical-reduction based remediation and bioremediation described in the prior art. The present invention has the further advantage that it can be used effectively either ex-situ or in-situ. A preferred embodiment of the present invention offers the further advantage of providing a means of promoting the bioremediation of contaminated sediments in-situ beneath bodies of natural water such as oceans, lakes, rivers, streams, and the like, and man-made water bodies such as waste-treatment lagoons and the like. The present invention also provides for significant cost savings relative to other means and methods for environmental remediation, as it can reduce or eliminate the need for excavation, pumpage, transportation, and/or off-site treatment of contaminated wastes, soil, or water.
The present invention is based upon discoveries from recent and ongoing experiments that several inter-related conditions must be achieved and maintained within the matrix of the contaminated media to enable the effective biodegradation of recalcitrant organic contaminants in the environment. Accordingly, the purpose of the present invention is to provide a solid-chemical composition and methods and means for the use thereof which specifically act to: (1) increase the biogeochemical reactivity and bioavailability of the contaminants; (2) create and maintain strongly anaerobic conditions by facilitating the biologically mediated removal of the available oxygen from the media; (3) create and maintain optimal Eh-pH conditions including strongly negative Eh conditions (Eh values less than xe2x88x92200 millivolts) and near neutral to slightly acidic pH conditions (6xe2x89xa7pHxe2x89xa78) which favor anaerobic, biologically mediated chemical-reduction reactions, e.g., the reductive dehalogenation of halogenated organic contaminants; and (4) provide means for maintaining conditions (1)-(3) for sufficiently long periods of time to enable the biologically mediated degradation, transformation, and/or detoxification reactions to proceed to the extent that the concentrations and/or toxicity of the contaminants are reduced to acceptable levels.
The disclosed solid-chemical compositions provide various forms of electrons, organic and inorganic electron acceptors and nutrients, organic and inorganic substrates for microorganisms as well as optional inorganic nutrient forms of nitrogen and phosphorus and optional chelating and acidifying agents. The discoveries disclosed herein indicate and/or strongly suggest that such contaminants can be effectively degraded, transformed and/or detoxified by indigenous, contaminant-degrading bacteria when the solid-chemical composition disclosed herein is applied to the contaminated media and the media are subsequently maintained under conditions favorable to the anaerobic microorganisms and the biogeochemical reactions mediated by these organisms, i.e., the media are kept moist or nearly saturated with water.
These and other objects and advantages of the present invention will become apparent to those skilled in the art following the detailed description of the invention which reveals the novel combination of solid chemical compositions described herein, and more particularly as defined by the appended claims.